Abstract: A dilation catheter having a balloon inflation shaft with an inflation lumen into which a stiffening wire extends and a guidewire shaft having a guide wire lumen adjacent to the balloon. The stiffening wire includes at least two stepped diameter reductions along its length to vary stiffness from a stiff proximal end providing improved pushability to a less stiff distal end providing improved trackability. A manifold at the inflation shaft proximal end includes a handle for adjusting the distance the stiffening wire extends into the inflation lumen to allow stiffness to be optimized. The handle includes a tubular flange frictionally engaging the manifold to prevent inadvertent handle movement. The balloon inflation shaft and guidewire shafts are bonded together in a manner producing an assembly having a circular cross section for improved connection to a circular balloon and improved catheter performance.